Which form of cellular transport moves substances against the concentration gradient?

• A. Facilitated diffusion
• B. Active transport
• C. Simple diffusion
• D. Passive transport

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the concept of a concentration gradient. A concentration gradient refers to the difference in the concentration of a substance between two areas. Substances naturally move from areas of high concentration to areas of low concentration (down the gradient) unless energy is applied.
2. Step 2: Review the types of cellular transport. Passive transport (including simple diffusion and facilitated diffusion) moves substances down the concentration gradient without requiring energy. Active transport, on the other hand, moves substances against the concentration gradient and requires energy input, typically in the form of ATP.
3. Step 3: Examine facilitated diffusion. Facilitated diffusion is a type of passive transport where substances move down the concentration gradient with the help of transport proteins, but it does not require energy.
4. Step 4: Analyze active transport. Active transport uses energy (ATP) to move substances against the concentration gradient, from areas of low concentration to areas of high concentration. This process often involves specific transport proteins, such as pumps.
5. Step 5: Compare the options provided in the question. Facilitated diffusion, simple diffusion, and passive transport all move substances down the concentration gradient without energy. Active transport is the only mechanism that moves substances against the concentration gradient and requires energy.